This invention relates to a method of control by phase angle which can be used in both the industrial and domestic fields. It particular, it respectively relates to the variable control of motors and light variators. The principle of the control by phase angle is to use an alternating power signal and to cause the switching in a load of this power signal at an appropriate instant, always the same, within a period of this alternating power signal. The setting of this appropriate instant with respect to an initial instant allows the power to be adjusted by synchronisation.
The frequency of the power signal used is an essential characteristic of the adjusting device with uses this principle. A first problem arises from the fact of the variation in the frequencies used: that is to say 60 Hz in America and 50 Hz in Europe and the rest of the world. The design of the corresponding devices must therefore be differentiated. Furthermore, the adjustment range of the phase control is derived according to the utilisation constraints of the integrated circuit which carries out this switching function. Thus, this adjustment range is in particular dependent on the clock frequency of the microcontroller used, on its temperature and on its supply voltage. Particularly if the sensitivity of the adjustment in not linear.
This type of disadvantage may not be harmful in the case where the variator used is a manually controlled one. Even so, the ease of use thereof is affected, particularly if the results of the control become much more sensitive at one place in the adjustment range than at another place.
On the other hand, in the field of servocontrol, the variation in sensitivity encountered throughout the adjustment range with phase control devices is not tolerable. This sensitivity conditions the activity of an actuator as a function of a control signal. In effect, if the control must be a servocontrol, the open loop gain of the servocontrol can then be different depending on whether the command value is situated in one place of the adjustment range or another. In order to avoid the hunting and oscillation phenomena of the servocontrol, it is necessary to take account of the maximum gain. The consequence of this is that, in the zones of the adjustment range where the gain is low, the reactivity of the servocontrol is also low. In some way the gathering of the activity of the actuator to the command value imposed on it is more or less rapid depending on the sensitivity of the adjustment range in question.
The purpose of the invention is to overcome this problem by providing in the control circuit a means of linearizing the activity of the actuator used (a lamp, a heating appliance, a motor or something else) with respect to the available control signal. This means is interposed between the command circuit and the actuator used. It will be shown that this procedure results in the solving of all the problems mentioned above.
The invention therefore relates to a method of control in which a periodic electrical signal is applied to an actuator by the intermediary of a switch with automatic cutoff, a control signal is produced, a time difference of an appropriate control instant is determined with respect to a characteristic instant of this periodic signal as a function of this control signal, the periodic closing of the switch is commanded at this appropriate instant in each period by applying this control signal to the switch, the activity of the actuator is adjusted by modifying the control signal, characterized in that the control signal is converted by a conversion into a different converted signal whose application causes a linear behaviour of the activity of the actuator as a function of this control signal and the converted signal is used to determine the time difference. When the activity is speed, the conversion is advantageously of the arcsine type. When the activity is power, the conversion is advantageously of the arcsine squared type.